1. Field of the Invention
This invention relates to a multi-function image recording apparatus provided with various functions.
2. Description of the Prior Art
Various apparatuses for recording images on sheets have heretofore been put into practical use. For example, there are copying apparatuses of the type in which the images of originals are recorded on sheets through a photosensitive medium or the like, and printers in which image information transformed into an electrical signal is reproduced as an image on a sheet by an impact system (the type system, the wire dot system or the like) or a non-impact system (the thermosensitive system, the ink jet system, the laser beam system or the like).
In recent years, from the demand for rationalization of office work, high productivity has been required of these image recording apparatuses. Particularly, improvement of the output speed (the number of sheets treated per unit time) has been strongly desired and the tendency toward higher speeds has developed.
However, the respective systems have their own speed limits and if an attempt is made to provide higher speeds than them, numerous problems will occur and to overcome them, a great effort such as development of a new technique will be required and the apparatus itself will become complicated and bulky as well as uneconomical. Taking a copying apparatus as an example, the image of an original is directed to a photosensitive medium and imaged to form a latent image which is developed into a visible image which in turn is transferred to a sheet and therefore, only one copy can be obtained for one cycle of original scanning. Accordingly, to realize a higher copying speed, the mechanical speed must be increased and this in turn may lead to insufficient sensitivity of the photosensitive medium or occurrence of problems such as vibration of the machine, noise and problems of durability. In contrast, if a countermeasure such as increasing the quantity of light of the lamp for illuminating the original is adopted, numerous problems including the temperature rise of the machine due to the heat emitted by the lamp will occur and complete solution of these problems will be difficult. Moreover, this difficulty increases in the fashion of an exponential function as the speed increases and therefore, the upper limit speed is naturally restricted by the balance with the merits provided by higher speed.
On the other hand, it has heretofore usually been the practice to record images on one surface of sheets, but there is now the desire to record images on both surfaces of sheets as in ordinary printed matters and decrease the number of sheets used from the viewpoint of saving of resources or filing space. In this regard as well, a system whereby sheets having images recorded on a first surface thereof are once accumulated and after the recording on the first surface is completed, the accumulated sheets are again fed and images are recorded on a second surface thereof has been proposed and put into practical use. However, this system is efficient when many sheets having a record of the same content are to be prepared, but it is very inefficient when many sheets having different records on both surfaces thereof are to be prepared. That is, when pages 1, 2, 3, 4, . . . are to be prepared, odd pages, i.e., pages 1, 3, 5, . . . must first be recorded on the first surface of the respective sheets, and then these sheets must be fed again and pages 2, 4, 6, . . . must be recorded on the second surface of the respective sheets. If, during the second feeding, multiplex feeding or jam of sheets should occur, the combination of the front and back pages will become different from a predetermined one and thus, recording will have to be done over again from the beginning. To avoid this, recording may be effected on each sheet in such a manner that the front and back surfaces of each sheet provide the front and back pages, respectively, but this takes much time for the re-feeding of sheets and the efficiency is reduced. Also, in the prior art method, the conveyance route of sheets has been complicated and further, the conveyance route has unavoidably involved the step of reversing sheets, and this has led to extremely low reliability of sheet conveyance.
In the tendency toward higher productivity, there is further a desire to record two types of information on one surface of a sheet in superposed relationship. Particularly, recently, coloring has advanced in various fields and there is also a desire to mix, for example, red record with black record (for example, to record the title in red) instead of black record only in a document to thereby make the document easier to see. In the prior art apparatuses, this has been made possible by a system using an ink ribbon or the like, but in copying apparatuses using the electrophotographic method or laser beam printers, the apparatus itself becomes very largescaled and therefore, apparatuses usable for ordinary office work have not yet been put into practical use. However, as a simple method, there is a system whereby recording is once effected in black, whereafter the developing device in the apparatus is changed from a black one to a red one and recording is again effected on the same surface, but this system has required much labor.
Also, where two types of information are to be recorded on one surface of the same sheet in superposed relationship, sufficient care must be taken of the image position accuracy, otherwise the resultant copy may become very unsightly due to color misregistration or deviation from a predetermined image recording frame. Furthermore, for example, when a transferred image is to be fixed on a sheet by a fixing system such as heat roller fixation, the heat or pressure imparted to the sheet accelerates deformation of the sheet and thus, great technical difficulties have been encountered as to the image position accuracy when two types of information are recorded on one surface of the sheet in superposed relationship.